[Made open: The state of international evidence-based research on Open Educational Resources (OER)].

Open Educational Resources (OER) are an integral part of the debate about the digitization of education. This article reviews the state of international empirical research on OER to identify possible desiderata for a future research agenda. A systematic mapping approach is used to map the empirical English-speaking research landscape. The results reveal that research concentrates on the higher education sector while only a few studies are available for the school sector. In terms of research methodology, quantitative studies are prevalent, mostly using surveys. The research interest of the studies lies in the perception of OER and their adoption and usage in educational practices. Open Textbooks and their comparative cost advantages or qualitative comparability with traditional educational material is a newly emerging field. Research gaps exist regarding usability and user-friendliness of OER repositories. Addressing these gaps could support the numerous initiatives of the German federal states to establish OER portals. Further research gaps were identified regarding the effects of the use of OER on pedagogical approaches and established educational practices.